The Redskins want Helu to win the second tailback job and provide versatility as well as big-play speed behind starter Alfred Morris. In order, the rotation has so far looked like this: Morris, Helu, Royster, Keiland Williams, Tristan Davis, Chris Thompson, and Jawan Jamison. Thompson and Jamison are rookies.

The Washington Times notes projected third-down back Roy Helu's "speed and elusiveness on the second level sets him apart" from Alfred Morris.

Helu offers considerably more straight-line speed and arguably just as much or more second-level wiggle than Washington's starter. Helu is vying to be the Skins' third-down back two seasons after racking up 49 receptions and rushing for 100 yards in three straight games late in his rookie year. Helu is the early favorite for Morris "handcuff" duties. He's worth a late-round fantasy pick.

Source: Washington Times Jul 29 - 3:40 PM

I've recently heard Royster being referred to as Alf's back-up in that, if Alf goes down, Royster becomes the 1st and 2nd down back - in spite of the "handcuff" comment above. Royster is more Alf-esque than Helu. Helu is the change-up.